The liquid is removed via a hypodermic needle through the stopper. The rubber stoppers come in a friendly orange and fit (13 mm) dia openings. The orange are 9/16" across the top, which has a dimple in the center, and 9/16" top to bottom. Why would you want them? They work perfect for mycology. Great for inoculation. Perfect for grain to grain transfer.

Orange Injection Port - Mycology